This invention relates to a screwdriver with a torque measuring scale and method of making the screwdriver, more particularly, it relates to the assembled parts which constitute the screwdriver for transmitting variable torque to a screw and for revealing and thereby measuring the magnitudes of those torques.
The prior art is already aware of screwdrivers which transmit various amounts of torque and measure those torques. They employ springs through which the torque is transmitted from a screwdriver handle to the screw and they do so by virtue of inducing tension in the spring when the handle is turned against resistance from the driven screw. A scale on the screwdriver reveals the amount of torque being applied to the screw.
Because of the inherent elasticity in the torquing spring, it is important the assembly with the spring be of an optimum arrangement to assure repeated usefulness of the screwdriver and repeated accuracy of torque indication.
The present invention achieves the aforementioned objectives in that it provides a screwdriver assembly wherein the spring and the mounting thereof result in the screwdriver providing accuracy in torque indication. Further, the accuracy is achievable in repeated uses and over a range of applied torques.
Further, this invention provides the screwdriver with features mentioned above and it does so with a screwdriver handle which is ergonomically appealing in its fit with the hand of the user such that maximum torque can be exerted by the hand and onto the screwdriver handle. Also, the handle provides for forceful gripping, even if and when itinerant liquid is on the handle. The strength of the spring, that is, the resistance of the spring during torquing, is selected to be compatible with the usual strength of an ordinary user""s hand. The handle is of a size so that it fits completely into the palm and fingers of the user""s hand.
Still further, the screwdriver of this invention is fluid-tightly sealed against entry of foreign matter for deposit between the moving parts, and thus the screwdriver maintains its accuracy and sterility for use in the medical field, such as in applications relative to bone screws.
Additionally, the screwdriver of this invention is readily and easily assembled, and it has a minimum of parts, and thus there is little opportunity for tampering which can upset the sealed condition or the accuracy of the torque production.
Even more so, the screwdriver of this invention is arranged for ready and accurate calibration and for limiting the amount of measurable torque transmitted and thereby avoid damage to the instrument. This is accomplished by employing a limit stop for governing the maximum amount of measurable torque, and there is a lost motion connection through which the torque can be transmitted.
Other objects and advantages will be apparent upon reading the following description in conjunction with the accompanying drawings.